Method for preparing aromatic secondary amino compound

ABSTRACT

Disclosed are 
     (1) a method for preparing an aromatic secondary amino compound which comprises reacting an N-cyclohexylideneamino compound in the presence of a hydrogen moving catalyst and a hydrogen acceptor by the use of a sulfur-free polar solvent and/or a cocatalyst, and 
     (2) a method for preparing an aromatic secondary amino compound which comprises reacting cyclohexanone or a nucleus-substituted cyclohexanone, an amine and a nitro compound corresponding to the amine in a sulfur-free polar solvent in the presence of a hydrogen moving catalyst, a cocatalyst being added or not added.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention relates to an improved method for preparing an aromatic secondary amino compound.

The aromatic secondary amino compound obtained by the method of the present invention is an extremely important industrial product such as a raw material for modifier of rubber and dyes.

b. Description of the Prior Art

As methods for preparing an aromatic secondary amino compound, these are known a method in which the reaction of toluidine is carried out in a liquid phase at 300° to 400° C. in the presence of a suitable self-condensation type reaction catalyst (BF₃, FeCl₂, a salt of an ammonium halogenide, or a mineral acid), and a method in which cresol is reacted with toluidine at 330° to 340° C. under pressure in the presence of triphenyl phosphite.

Other methods for preparing the aromatic secondary amino compound are also known which comprise the dehydrogenation reaction of an N-cyclohexylideneamino compound. For example, there are a method for obtaining N-cyclohexylidene-N' -isopropylphenylenediamine at a temperature of 350° C. or less in the presence of a dehydrogenation catalyst (British Patent No. 989257); a method in which reaction is carried out in a gaseous phase, while oxygen or an oxygen-containing gas is fed at 300° to 450° C. in the presence of an oxidizing catalyst such as silica or alumina (Japanese Patent Application Laid-open No. 49924/1974); a method for obtaining 4-methyldiphenylamine by reaction at 300° to 500° C. in the presence of a dehydrogenation catalyst selected from the group consisting of nickel, platinum, palladium and copper-chromium alloy (Japanese Patent Application Laid-open No. 49925/1974); and a method for preparing an amino compound by the use of a specific nickel/chromium catalyst (Japanese Patent Publication No. 4623/1982).

Still other methods are already known in which a nitro compound is used as a hydrogen acceptor in the presence of a hydrogen moving catalyst to produce an amine in the system, and a nucleus-substituted cyclohexanone is simultaneously reacted with the amine to prepare an aromatic secondary amino compound. For example, there are a method for obtaining p-ethoxydiphenylamine by reacting p-nitrophenetole with a large excess of cyclohexanone in the presence of a palladium catalyst (British Patent No. 975097); a method for obtaining 2,6-dimethyldiphenylamine by reacting 1/3 mol of 2,6-dimethylaniline, 2/3 mol of 2,6-dimethylnitrobenzene, and cyclcohexanone in the presence of a palladium catalyst, the amount of cyclohexanone being 10% in excess of the total of 2,6-dimethylaniline and 2,6-dimethylnitrobenzene (British Patent No. 989257); and a method for preparing a diphenylamine derivative by reacting 2-(alkyl or alkoxy)-4-alkoxynitrobenzene, 2-(alkyl or alkoxy)-4-alkoxyaniline and cyclohexanone in the presence of a palladium catalyst (Japanese Patent Application Laid-open No. 117214/1993).

However, these conventional methods have drawbacks of (1) severe reaction conditions, (2) a low reaction rate, and (3) a low yield. For these reasons, they are not industrially satisfactory manufacturing methods.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an industrially improved method for preparing an aromatic secondary amino compound from an N-cyclohexylidene amino compound or cyclohexanone (inclusive of a nucleus-substituted compound), and according to this method, the above-mentioned problems can be solved.

As a result of various investigations, it has been found that the aromatic secondary amino compound can be obtained under extremely moderate conditions in a high yield by (1) using a sulfur-free polar solvent and/or a cocatalyst at the time of the dehydrogenation reaction of an N-cyclohexylideneamino compound in the presence of a hydrogen moving catalyst and a hydrogen acceptor, or (2) reacting cyclohexanone or a nucleus-substituted cyclohexanone with an amine in a sulfur-free polar solvent in the presence of a hydrogen moving catalyst by the use of a nitro compound corresponding to the amine as a hydrogen acceptor, or adding a specific cocatalyst to this system and then reacting the same. In consequence, the present invention has been attained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first aspect of the present invention is directed to a method for preparing an aromatic secondary amino compound represented by the formula (2) ##STR1## (wherein each R is a hydrogen atom, alkyl group, alkoxy group, amino group, hydroxyl group or fluorine; n is an integer of from 0 to 5; and R' is an alkyl group, phenyl group, benzyl group, naphthyl group, furyl group, furfuryl group or cyclohexyl group, and R' may be substituted by an alkyl group, alkoxy group, phenyl group, phenoxy group, cyclohexyl group, substituted amino group, carboxyl group, hydroxyl group or fluorine)

which comprises the step of subjecting, to a dehydrogenation reaction, an N-cyclohexylideneamino compound represented by the formula (1) ##STR2## (wherein R, R' and n are defined above) in the presence of a hydrogen moving catalyst and a hydrogen acceptor, said method being characterized in that a sulfur-free polar solvent is used at the time of the dehydrogenation reaction.

The N-cyclohexylideneamino compound which is used as a starting material can be easily synthesized from an amine (or its derivative having an amino group with a substituent) and cyclohexanone or its derivative in accordance with a known process.

Examples of the alkyl group represented by R in the formula (1) include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, phenylmethyl, aminomethyl, hydroxymethyl and fluoromethyl, and above all, methyl and ethyl are preferable.

Examples of the alkoxy group include methoxy, ethoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, dodecyloxy, hexadecyloxy, aminomethoxy and fluoromethoxy, and above all, methyloxy, ethyloxy are preferable.

Examples of the amino group include amino, methylamino, ethylamino, propylamino, isopropylamino, butylamino, isobutylamino, tert-butylamino, pentylamino, dimethylamino, diethylamino, cyclohexylamino and acetylamino.

Examples of the alkyl group represented by R' in the formula (1) include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, aminomethyl, aminoethyl, aminopropyl, 2-aminopropyl, 3-aminopropyl, aminobutyl and hydoxyethyl.

Examples of the phenyl group include phenyl, o-methylphenyl, m-methylphenyl, p-methylphenyl, p-ethylphenyl, p-propylphenyl, p-isopropylphenyl, p-butylphenyl, p-tert-butylphenyl, p-pentylphenyl, p-hexylphenyl, p-heptylphenyl, p-octylphenyl, p-nonylphenyl, p-decylphenyl, p-dodecylphenyl, p-hexadecylphenyl, 3,4-dimethylphenyl, 2,3-dimethylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, p-methoxyphenyl, p-ethoxyphenyl, p-butoxyphenyl, p-pentyloxyphenyl, p-hexyloxyphenyl, p-heptyloxyphenyl, p-octyloxyphenyl, p-nonyloxyphenyl, p-phenyloxyphenyl, p-trioxyphenyl, p-acetylphenyl, p-benzoylphenyl, p-aminophenyl, p-methylaminophenyl, p-ethylaminophenyl, p-butylaminophenyl, p-tert-butylaminophenyl, p-octylaminophenyl , p-dodecylaminophenyl, p-cyclohexylphenyl, p-methylcyclohexylphenyl, p-ethylcyclohexylphenyl, p-propylcyclohexylphenyl, p-hydroxyphenyl, p-carboxyphenyl and p-fluorophenyl, and phenyl and p-methylphenyl are preferable.

Examples of the benzyl group include benzyl, o-methylbenzyl, m-methylbenzyl, p-methylbenzyl, p-ethylbenzyl, p-propylbenzyl, p-isopropylbenzyl, p-butylbenzyl, p-tert-butylbenzyl, p-pentylbenzyl, p-hexylbenzyl, p-heptylbenzyl, p-octylbenzyl, p-nonylbenzyl, p-decylbenzyl, p-dodecylbenzyl, p-hexadecylbenzyl, p-acetylbenzyl, 3,4-dimethylbenzyl, 2,3-dimethylbenzyl, 2,6-dimethylbenzyl, 2,4,6-trimethylbenzyl, p-methoxybenzyl, p-ethoxybenzyl, p-butoxybenzyl, p-pentyloxybenzyl, p-hexyloxybenzyl, p-heptyloxybenzyl, p-octyloxybenzyl, p-nonyloxybenzyl, p-phenyloxybenzyl, p-tolyloxybenzyl, p-benzoylbenzyl, p-methylaminobenzyl, p-ethylaminobenzyl, p-butylaminobenzyl, p-tert-butylaminobenzyl, p-octylaminobenzyl, p-dodecylaminobenzyl, p-cyclohexylbenzyl, p-methylcyclohexylbenzyl, p-ethylcyclohexylphenyl, p-propylcyclohexylbenzyl, p-hydroxybenzyl, p-carboxybenzyl and p-fluorobenzyl.

Examples of the cyclohexyl group include cyclohexyl, o-methylcyclohexyl, m-methylcyclohexyl, p-methylcyclohexyl, p-ethylycyclohexyl, p-propylcyclohexyl, p-isopropylcyclohexyl, p-butylcyclohexyl, p-tert-butylcyclohexyl, p-pentylcyclohexyl, p-hexylcyclohexyl, p-heptylcyclohexyl, p-octylcyclohexyl, p-nonylcyclohexyl, p-decylcyclohexyl, p-dodecylcyclohexyl, p-hexadecylcyclohexyl, p-acetylcyclohexyl, 3,4-dimethylcyclohexyl, 2,3-dimethylcyclohexyl, 2,6-dimethylcyclohexyl, 2,4,6-trimethylcyclohexyl, p-methoxycyclohexyl, p-ethoxycyclohexyl, p-butoxycyclohexyl, p-pentyl oxycyclohexyl, p-hexyloxycyclohexyl, p-heptyloxycyclohexyl, p-octyloxycyclohexyl and p-nonyloxycyclohexyl.

The preferred compounds of formula (1) are as follows:

1. N-(cyclohexylidene)methylamine

2. N-(4-methylcyclohexylidene)methylamine

3. N-(4-methyloxycyclohexylidene)methylamine

4. N-(cyclohexylidene)aniline

5. N-(2-methylcyclohexylidene)aniline

6. N-(3-methylcyclohexylidene)aniline

7. N-(4-methylcyclohexylidene)aniline

8. N-(4-ethylcyclohexylidene)aniline

9. N-(2,6-dimethylcyclohexylene)aniline

10. N-(4-methyloxycyclohexylidene)aniline

11. N-(4-fluorocyclohexylidene)aniline

12. (4-hydroxycyclohexylidene)aniline

13. N-(cyclohexylidene)-2-methylaniline

14. N-(2-methylcyclohexylidene)-2-methylaniline

15. N-(3-methylcyclohexylidene)-2-methylaniline

16. N-(4-methylcyclohexylidene)-2-methylaniline

17. N-(4-ethylcyclohexylidene)-2-methylaniline

18. N-(2,6-dimethylcyclohexylidene)-2-methylaniline

19. N-(4-methyloxycyclohexylidene)-2-methylaniline

20. N-(4-fluorocyclohexylidene)-2-methylaniline

21. N-(4-hydroxycyclohexylidene)-2-methylaniline

22. N-(cyclohexylidene)-3-methylaniline

23. N-(2-methylcyclohexylidene)-3-methylaniline

24. N-(3-methylcyclohexylidene)-3-methylaniline

25. N-(4-methylcyclohexylidene)-3-methylaniline

26. N-(4-ethylcyclchexylidene)-3-methylaniline

27. N-(2,6-dimethylcyclohexylidene)-3-methylaniline

28. N-(4-methyloxycyctohexylidene)-3-methylaniline

29. N-(4-fluorocyclohexylidene)-3-methylaniline

30. N-(4-hydroxycyclohexylidene)-3-methylaniline

31. N-(cyclohexylidene)-4-methylaniline

32. N-(2-methylcyclohexylidene)-4-methylaniline

33. N-(3-methylcyclohexylidene)-4-methylaniline

34. N-(4-methylcyclohexylidene)-4-methylaniline

35. N-(4-ethylcyclohexylidene)-4-methylaniline

36. N-(2,6-dimethylcyclohexylidene)-4-methylaniline

37. N-(4-methyloxycyclohexylidene)-4-methylaniline

38. N-(4-fluorocyclohexylidene)-4-methylaniline

39. (4-hydroxycyclohexylidene)-2-methylaniline

40. N-(cyclohexylidene)-2,4-dimethylaniline

41. N-(2-methylcyclohexylidene)-2,4-dimethylaniline

42. N-(3-methylcyclohexylidene)-2,4-dimethylaniline

43. N-(4-methylcyclohexylidene)-2,4-dimethylaniline

44. N-(4-ethylcyclohexylidene)-2,4-dimethylaniline

45. N-(2,6-dimethylcyclohexylidene)-2,4-(dimethylaniline)

46. N-(4-methyloxycyclohexylidene)-2,4-(dimethylaniline)

47. N-(4-fluorocyclohexylidene)-2,4-dimethylaniline

48. N-(4-hydroxycyclohexylidene)-2,4-dimethylaniline

49. N-(cyclohexylidene)-4-methoxyaniline

50. N-(2-methylcyclohexylidene)-4-methoxyaniline

51. N-(3-methylcyclohexylidene)-4-methoxyaniline

52. N-(4-methylcyclohexylidene)-4-methoxyaniline

53. N-(4-ethylcyclohexylidene)-4-methoxyaniline

54. N-(2,6-dimethylcyclohexylidene)-4-methoxyaniline

55. N-(4-methyloxycyclohexylidene)-4-methoxyaniline

56. N-(4-fluorocyclohexylidene)-4-methoxyaniline

57. N-(4-hydroxycyclohexylidene)-4-methoxyaniline

58. N-(cyclohexylidine)-4-hydroxyaniline

59. N-(2-methylcyclohexylidene)-4-hydroxyaniline

60. N-(3-methylcyclohexylidene)-4-hydroxyaniline

61. N-(4-methylcyclohexylidene)-4-hydroxyaniline

62. (4-ethylcyclohexylidene)-4-hydroxyaniline

63. N-(2,6-dimethylcyclohexylidene)-4-hydroxyaniline

64. N-(4-methyloxycyclohexylidene)-4-hydroxyaniline

65. N-(4-fluorocyclohexylidene)-4-hydroxyaniline

66. N-(4-hydroxycyclohexylidene)-4-hydroxyaniline

67. N-(cyclohexylidene)benzylamine

68. N-(2-methylcyclohexylidene)benzylamine

69. N-(3-methylcyclohexylidene)benzylamine

70. N-(4-methylcyclohexylidene)benzylamine

71. N-(4-ethylcyclohexylidene)benzylamine

72. N-(2,6-dimethylcyclohexylidene)benzylamine

73. N-(4-methyloxycyclohexylidene)benzylamine

74. N-(4-fluorocyclohexylidene)benzylamine

75. N-(4-hydroxycyclohexylidene)benzylamine

76. N-(cyclohexylidene)cyclohexyl

77. N-(2-methylcyclohexylidene)cyclohexyl

78. N-(3-methylcyclohexylidene)cyclohexyl

79. N-(4-methylcyclohexylidene)cyclohexyl

80. N-(4-ethylcyclohexylidene)cyclohexyl

81. N-(2,6-dimethylcyclohexylidene)cyclohexyl

82. N-(4-methyloxycyclohexylidene)cyclohexyl

83. N-(4-fluorocyclohexylidene)cyclohexyl

84. N-(4-hydroxycyclohexylidene)cyclohexyl

85. N-(cyclohexylidene)-4-fluoroaniline

86. N-(2-methylcyclohexylidene)-4-fluoroaniline

87. N-(3-methylcyclohexylidene)-4-fluoroaniline

88. N-(4-methylcyclohexylidene)-4-fluoroaniline

89. N-(4-ethylcyclohexylidene)-4-fluroaniline

90. N-(2,6-dimethylcyclohexylidene)-4-fluroaniline

91. N-(4-methyloxycyclohexylidene)-4-fluoroaniline

92. N-(4-fluorocyclohexylidene)-4-fluoroaniline

93. N-(4-hydroxycyclohexylidene)-4-fluoroaniline

94. N-(2-methylcyclohexylidene)methylamine

95. N-(3-methylcyclohexylidene)methylamine

96. N-(4-ethylcyclohexylidene)methylamine

97. N-(2,6-dimethylcyclohexylidene)methylamine

98. N-(4-methyloxycyclohexylidene)methylamine

99. N-(4-fluorocyclohexylidene)methylamine

100. N-(4-hydroxycyclohexylidene)methylamine

101. N-(cyclohexylidene)-4-phenoxyaniline

102. N-(2-methylcyclohexylidene)-4-phenoxyaniline

103. N-(3-methylcyclohexylidene)-4-phenoxyaniline

104. N-(4-methylcyclohexylidene)-4-phenoxyaniline

105. N-(4-ethylcyclohexylidene)-4-phenoxyaniline

106. N-(2,6-dimethylcyclohexylidene)-4-phenoxyaniline

107. N-(4-methyloxycyclohexylidene)-4-phenoxyaniline

108. N-(4-fluorocyclohexylidene)-4-phenoxyaniline

109. N-(4-hydroxycyclohexylidene)-4-phenoxyaniline

110. N-(cyclohexylidene)-4-fluoroaniline

111. N-(2-methylcyclohexylidene)-4-fluoroaniline

112. N-(3-methylcyclohexylidene)-4-fluroaniline

113. N-(4-methylcyclohexylidene)-4-fluroaniline

114. N-(4-ethylcyclohexylidene)-4-fluoroaniline

115. N-(2,6-dimethylcyclohexylidene)-4-fluoroaniline

116. N-(4-methyloxycyclohexylidene)-4-fluoroaniline

117. N-(4-fluorocyclohexylidene)-4-fluoroaniline

118. N-(4- hydroxycyclohexylidene)-4-fluoroaniline

As the hydrogen moving catalyst, there can be used any known hydrogen moving catalyst. Typical examples of the hydrogen moving catalyst include Raney nickel, reduced nickel and nickel supporting catalysts obtained by supporting nickel on various carriers such as diatomaceous earth, alumina, pumice, silica gel and acidic terra abla; cobalt catalysts such as Raney cobalt, reduced cobalt, cobalt and cobalt-carrier catalysts; copper catalysts such as Raney copper, reduced copper and copper-carrier catalysts; palladium catalysts such as palladium black, palladium oxide, colloidal palladium, palladium-carbon, palladium-barium sulfate and palladium-barium carbonate; platinum catalysts such as platinum black, colloidal platinum, platinum sponge, platinum oxide, platinum sulfide, platinum-carbon and platinum-carrier catalysts; rhodium catalysts such as colloidal rhodium, rhodium-carbon and rhodium oxide; a platinum group catalyst such as a ruthenium catalyst; rhenium catalysts such as dirhenium heptaoxide and rhenium-carbon; a copper chromium oxide catalyst; a molybdeum oxide catalyst; a vanadium oxide catalyst; and a tungsten oxide catalyst. Among these catalysts, the palladium catalyst is preferable. In particular, the palladium-carrier catalyst is preferable. Above all, the palladium-carbon and palladium-alumina are most preferable.

The amount of the hydrogen moving catalyst is usually in the range of from 0.001 to 1.0 gram atom, preferably from 0.002 to 0.2 gram atom in terms of a metallic atom per gram molecule of the N-cyclohexylideneamino compound.

In the first aspect of the present invention, any of various reducing materials is used as a hydrogen acceptor. Examples of the hydrogen acceptor include olefin compounds such as 1-octene, allylbenzene and crotonic acid; nitro compounds such as 2,6-dimethylnitrobenzene, p-amylnitrobenzene, p-hexylnitrobenzene, p-octylnitrobenzene, p-sec-octylnitrobenzene, p-tert-octylnitrobenzene, p-nonylnitrobenzene, p-decylnitrobenzene, p-ethoxynitrobenzene, o-ethoxynitrobenzene, 2,6-dimethyl-4-aminonitrobenzene, nitrobenzene, p-dinitrobenzene, m-dinitrobenzene, 4-nitrodiphenyl, p-phenoxynitrobenzene, p-cyclohexylnitrobenzene, p-benzylnitrobenzene, nitromethane, 2-nitropropane, 1-nitronaphthalene, 2-, 3- and 4-nitrotoluenes, 4-nitroanisole, p-propylnitrobenzene, m-ethylnitrobenzene, 4-nitrobenzonitrile, p-nitroacetoanilide, 4-nitrobenzoic acid and nitrocyclohexane; phenols, for example, alkylphenols such as phenol, methylphenol, ethylphenol, isopropylphenol, butylphenol, 2,4-dimethylphenol, 2,4,6-trimethylphenol and 2,6-di-tert-butyl-4-methylphenol as well as alkoxyphenols such as 3-methoxyphenol and 4-methoxyphenol.

However, in the case that the phenol is selected, it must be used in large quantities and there is the tendency that the amounts of by-products increase. It is particularly preferable to use nitrobenzene in the above-mentioned nitro compounds as the hydrogen acceptor, because nitrobenzene can be utilized as the material of N-cyclohexylideneaniline.

The amount of the hydrogen acceptor to be used depends upon its kind, but it is 5 equivalents of the hydrogen acceptor to the N-cyclohexylideneamino compound. Particularly in the case of the olefin or the nitro compound, the amount of the hydrogen acceptor is an equivalent or 50% excess of the N-cyclohexylideneamino compound. When the hydrogen acceptor is short, the by-product of N-cyclohexylamine tends to increase. As the hydrogen acceptor, the olefin or the nitro compound is preferable from the viewpoint of the volume efficiency of a reactor.

Examples of the sulfur-free polar solvent to be used include N,N-dimethyl formamide, N,N-dimethylacetamide, tetramethylurea, methyl isobutyl ketone, tetrahydrofuran, dioxane, 1,3-dimethylimidazolizinone, glymes such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, methyl salicylate, phenyl and phenols, for example, alkylphenols such as methylphenol and 2,4,6-trimethylphenol as well as alkoxyphenols such as 3-methoxyphenol and 4-methoxyphenol. If necessary, they may be used in combination of two or more thereof. Dimethyl sulfoxide and sulfolane are similarly within the category of the polar solvents, but they are not used because they contain sulfur which is poisonous to the dehydrogenation catalyst.

The amount of the sulfur-free polar solvent to be used is preferably 0.05-3.0 times by weight, more preferably 0.15-1.5 times by weight as much as that of the N-cyclohexylideneamino compound.

In placing the starting materials in a reactor, it is a preferable manner that the solvent and the catalyst are previously placed in the reactor and mixed, and the N-cyclohexylideneamine compound and the hydrogen acceptor are then simultaneously dropped into the reactor to carry out the above-mentioned reaction. Needless to say, alternatively, the N-cyclohexylideneamino compound and the hydrogen acceptor may be first mixed and then added into the reactor.

In the above-mentioned dehydrogenation reaction of the N-cyclohexylideneamino compound in the presence of the hydrogen moving catalyst and the hydrogen acceptor, an alkali metal compound and/or an alkaline earth metal compound can be added as a cocatalyst to the reaction system irrespective of the presence of the sulfur-free polar solvent. This is also one embodiment of the first aspect of the present invention.

Usable examples of the alkali metal compound and/or the alkaline earth metal compound which can be added as the cocatalyst are hydroxides, carbonates, bicarbonates and the like of alkali metals and alkaline earth metals. Typical examples of these compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate and sodium hydrogen carbonate. Above all, sodium hydroxide and potassium hydroxide are preferable. These cocatalysts may be used singly or in combination of two or more thereof. The cocatalyst does not have to be added to the reaction system separately from the above-mentioned dehydrogenation catalyst. For example, after a noble metal supporting catalyst has been prepared, a salt, a hydroxide or the like of an alkali metal and/or an alkaline earth metal may be additionally supported as the alkali metal component and/or the alkaline earth metal component on the noble metal supporting catalyst, and the thus formed catalyst may be used.

The amount of the cocatalyst is preferably in the range of from 2 to 30% by weight, more preferably from 5 to 20% by weight, in terms of the alkali metal and/or the alkaline earth metal, based on the weight of the catalyst metal. If the amount of the cocatalyst is in excess of this range, a reaction rate tends to deteriorate, and conversely if it is less than the range, a yield is low.

It is advantageous that the reaction is carried out under the removal of water, and thus a technique is suitable in which water is removed from the reaction mixture while azeotropic distillation is done by the use of a solvent such as benzene, toluene or xylene.

The temperature at the reaction is usually in the range of from 120° to 250° C., preferably from 140° to 200° C.

The mixture obtained by the above-mentioned method is treated in an ordinary manner such as distillation, crystallization or extraction. For example, the solution in which the reaction has already been brought to an end is filtered to separate the catalyst therefrom. The thus recovered catalyst can be reused. The resultant filtrate is concentrated to recover the solvent. The produced aromatic secondary amino compound in the reactor can be directly used without any treatment, but if necessary, it may be purified by distillation, crystallization or the like.

The second aspect of the present invention is directed to a methyl for preparing an aromatic secondary amino compound represented by the formula (2) ##STR3## (wherein each R is a hydrogen atom, alkyl group, alkoxy group, amino group, hydroxyl group or fluorine; R' is an alkyl group, phenyl group, benzyl group, naphthyl group, furyl group, furfuryl group or cyclohexyl group, and R' may be substituted by an alkyl group, alkoxy group, phenyl group, phenoxy group, cyclohexyl group, substituted amino group, carboxyl group, hydroxyl group or fluorine; and n is an integer of from 0 to 5)

which comprises the step of reacting cyclohexanone or a nucleus-substituted cyclohexanone represented by the formula (3) ##STR4## (wherein R is defined above), an amine represented by the formula (4)

    R'--NH.sub.2                                               (4)

(wherein R' is defined above), and

a nitro compound corresponding to the amine and represented by the formula (5)

    R'--NO.sub.2                                               (5)

(wherein R' is defined above)

as a hydrogen acceptor in a sulfur-free polar solvent in the presence of a hydrogen moving catalyst.

That is, the second aspect of the present invention is directed to a method for preparing an aromatic secondary amino compound which is characterized by comprising the step of reacting cyclohexanone or a nucleus-substituted cyclohexanone, an amine and a nitro compound as a hydrogen acceptor corresponding to the amine in a sulfur-free polar solvent in the presence of a hydrogen moving catalyst.

Examples of the alkyl group represented by R' in the formulae (4) and (5) include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, aminomethyl, aminoethyl, aminopropyl, 2-aminopropyl, 3-aminopropyl, aminobutyl and hydoxyethyl.

Examples of the phenyl group include phenyl, o-methylphenyl, m-methylphenyl, p-methylphenyl, p-ethylphenyl, p-propylphenyl, p-isopropylphenyl, p-butylphenyl, p-tert-butylphenyl, p-pentylphenyl, p-hexylphenyl, p-heptylphenyl, p-octylphenyl, p-nonylphenyl, p-decylphenyl, p-dodecylphenyl, p-hexadecylphenyl, 3,4-dimethylphenyl, 2,3-dimethylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, p-methoxyphenyl, p-ethoxyphenyl, p-butoxyphenyl, p-pentyloxyphenyl, p-hexyloxyphenyl, p-heptyloxyphenyl, p-octyloxyphenyl, p-nonyloxyphenyl, p-phenyloxyphenyl, p-trioxyphenyl, p-acetylphenyl, p-benzoylphenyl, p-aminophenyl, p-methylaminophenyl, p-ethylaminophenyl, p-butylaminophenyl, p-tert-butylaminophenyl, p-octylaminophenyl, p-dodecylaminophenyl, p-cyclohexylphenyl, p-methylcyclohexylphenyl, p-ethylcyclohexylphenyl, p-propylcyclohexylphenyl, p-hydroxyphenyl, p-carboxyphenyl and p-fluorophenyl, and phenyl and p-methylphenyl are preferable.

Examples of the benzyl group include benzyl, o-methylbenzyl, m-methylbenzyl, p-methylbenzyl, p-ethylbenzyl, p-propylbenzyl, p-isopropylbenzyl, p-butylbenzyl, p-tert-butylbenzyl, p-pentylbenzyl, p-hexylbenzyl, p-heptylbenzyl, p-octylbenzyl, p-nonylbenzyl, p-decylbenzyl, p-dodecylbenzyl, p-hexadecylbenzyl, p-acetylbenzyl, 3,4-dimethylbenzyl, 2,3-dimethylbenzyl, 2,6-dimethylbenzyl, 2,4,6-trimethylbenzyl, p-methoxybenzyl, p-ethoxybenzyl, p-butoxybenzyl, p-pentyloxybenzyl, p-hexyloxybenzyl, p-heptyloxybenzyl, p-octyloxybenzyl, p-nonyloxybenzyl, p-phenyloxybenzyl, p-tolyloxybenzyl, p-benzoylbenzyl, p-methylaminobenzyl, p-ethylaminobenzyl, p-butylaminobenzyl, p-tert-butylaminobenzyl, p-octylaminobenzyl, p-dodecylaminobenzyl, p-cyclohexylbenzyl, p-methylcyclohexylbenzyl, p-ethylcyclohexylbenzyl, p-propylcyclohexylbenzyl, p-hydroxybenzyl, p-carboxybenzyl and p-fluorobenzyl.

Examples of the cyclohexyl group include cyclohexyl, o-methylcyclohexyl, m-methylcyclohexyl, p-methylcyclohexyl, p-ethylcyclohexyl , p-propylcyclohexyl, p-isopropylcyclohexyl, p-butylcyclohexyl, p-tert-butylcyclohexyl, p-pentylcyclohexyl, p-hexylcyclohexyl, p-heptylcyclohexyl, p-octylcyclohexyl , p-nonylcyclohexyl, p-decylcyclohexyl, p-dodecylcyclohexyl , p-hexadecylcyclohexyl, p-acetylcyclohexyl, 3,4-dimethylcyclohexyl, 2,3-dimethylcyclohexyl, 2,6-dimethylcyclohexyl, 2,4,6-trimethylcyclohexyl, p-methoxycyclohexyl, p-ethoxycyclohexyl, p-butoxycyclohexyl, p-pentyloxycyclohexyl, p-hexyloxycyclohexyl, p-heptyloxycyclohexyl, p-octyloxycyclohexyl and p-nonyloxycyclohexyl.

The preferred compounds of formula (3) are as follows:

1. cyclohexanone

2. 2-methylcyclohexanone

3. 3-methylcyclohexanone

4. 4-methylcyclohexanone

5. 4-ethylcyclohexanone

6. 4-octylcyclohexanone

7. 2,6-dimethylcyclohexanone

8. 2,4-dimethylcyclohexanone

9. 4-phenylcyclohexanone

10. 4-phenylmethylcyclohexanone

11. 4-phenyloxycyclohexanone

12. 4-methyloxycyclohexanone

13. 4-nonyloxycyclohexanone

14. 4-methylaminocyclohexanone

15. 4-dimethylaminocyclohexanone

16. 4-acetylaminocyclohexanone

17. 4-fluorocyclohexanone

18. 4-hydroxycyclohexanone

The preferred compounds of formula (4) are as follows:

1. methylamine

2. ethylamine

3. aniline

4. 2-methylaniline

5. 3-methylaniline

6. 4-methylaniline

7. 4-ethylaniline

8. 4-nonylaniline

9. 2,6-dimethylaniline

10. 2,4-dimethylaniline

11. 2,4,6-trimethylaniline

12. 4-methoxyaniline

13. 2-methyl-4-methoxyaniline

14. 4-acetylaniline

15. 4- aminoacetoanilide

16. 4-methylaminoaniline 7. 4-cyclohexylaniline

18. 4-hydroxyaniline

19. 4-carboxyaniline

20. benzylamine

21. 4-methylbenzylamine

22. 4-octylbenzylamine

23. 2,4-dimethylbenzylamine

24. 4-methoxybenzylamine

25. cyclohexylamine

26. 4-methylcyclohexylamine

27. 4-methyloxycycloamine

28. 2-naphthylamine

29. furfurylamine

30. 4-fluoroaniline

31. 4-aminodiphenylether

The preferred compounds of formula (5) are as follows:

1. nitromethane

2. nitroethane

3. nitrobenzene

4. 2-nitrotoluene

5. 3-nitrotoluene

6. 4-nitrotoluene

7. 4-ethylnitrobenzene

8. 4-nonylnitrobenzene

9. 2,6-dimethylnitrobenzene

10. 2,4-dimethylnitrobenzene

11. 2,4,6-trimethylnitrobezene

12. 4-methyoxynitrobenzene

13. 2-methyl -4-methoxynitrobenzene

14. 4-acetylnitrobezene

15. 4-nitroacetoanilide

16. 4-methylaminonitrobenzene

17. 4-cyclohexylnitrobenzene

18. 4-hydroxynitrobenzene

19. 4-carboxynitrobenzene

20. nitrobenzyl

21. 4-methylnitrobenzyl

22. 4-octylnitrobenzyl

23. 2,4-dimethylnitrobenzyl

24. 4-methoxynitrobenzyl

25. nitrocyclohexanone

26. 4-methylnitrocyclohexanone

27. 4-methoxynitrocyclohexanone

28. 2-nitronaphthalene

29. nitrofurfuryl

30. 4-fluoronitrobenzene

31. 4-nitrodiphenylether

In the present invention, a molar ratio of the cyclohexanone or the nulcleus-substituted cyclohexanone represented by the formula (3): the amine represented by the formula (4): the nitro compound represented by the formula (5) is usually 3:1:2, and this ratio can be suitably altered on the basis of the given values. The nitro compound behaves as the hydrogen acceptor to produce the amine in the reaction system, arid this amine causes a condensation reaction with the cyclohexanone or the nucleus-substituted cyclohexanone which is another starting material, to produce a Schiff base. Afterward, the Schiff base is subjected to dehydrogenation, thereby producing an aromatic secondary amino compound. In the dehydrogenation of the Schiff base, hydrogen is generated, and 2/3 mol of the nitro compound per mol of the Schiff base can be converted into the amine by the thus generated hydrogen.

Therefore, in order to completely effectively utilize the hydrogen generated in the system, it is necessary to react the cyclohexanone or the nucleus-substituted cyclohexanone and the nitro compound in a molar ratio of 3:2. In this case, however, the excessive amount of the cyclohexanone or the, nucleus-substituted cyclohexanone further reacts with the aromatic secondary amino compound produced in the system, so that an aromatic tertiary amino compound tends to be produced as a by-product. Conversely, if the amount of the nitro compound is excessive, a reaction rate tends to deteriorate inconveniently. For the purpose of avoiding these drawbacks, it is preferable that a molar ratio of the cyclohexanone or the nucleus-substituted cyclohexanone:the amine compound:the nitro compound is 3:1:2, and more preferably, a molar ratio of the sum of the nitro compound and the amine compound to the cyclohexanone or the nucleus-substituted cyclohexanone is in the range of from 0.9 to 1.2.

As the hydrogen moving catalyst which can be used in the method of the present invention, there can be used any known hydrogen moving catalyst. Typical examples of the hydrogen moving catalyst include Raney nickel, reduced nickel and nickel supporting catalysts obtained by supporting nickel on various carriers such as diatomaceous earth, alumina, pumice, silica gel and acidic terra abla; cobalt catalysts such as Raney cobalt, reduced cobalt, cobalt and cobalt-carrier catalysts; copper catalysts such as Raney copper, reduced copper and copper-carrier catalysts; palladium catalysts such as palladium black, palladium oxide, colloidal palladium, palladium-carbon, palladium-barium sulfate and palladium-barium carbonate; platinum catalysts such as platinum black, colloidal platinum, platinum sponge, platinum oxide, plating,m sulfide, and platinum-carrier catalysts such as platinum-carbon; rhodium catalysts such as colloidal rhodium, rhodium-carbon and rhodium oxide; a platinum group catalyst such as a ruthenium catalyst; rhenium catalysts such as dirhenium heptaoxide and rhenium-carbon; a copper chromium oxide catalyst; a molybdenum oxide catalyst; a vanadium oxide catalyst; and a tungsten oxide catalyst. Among these catalysts, the palladium catalyst is preferable. In particular, the palladium-carrier catalyst is preferable. Above all, the palladium-carbon and palladium-alumina are most preferable.

The amount of the hydrogen moving catalyst to be used is usually in the range of from 0.001 to 1.0 gram atom, preferably from (0.002 to 0.2 gram atom in terms of a metallic atom per gram molecule of the amine.

The method of the present invention is characterized by using a sulfur-free polar solvent. Examples of the sulfur-free polar solvent include N,N-dimethylformamide, N,N-dimethylacetamide, tetramethylurea, methyl isobutyl ketone, tetrahydrofuran, dioxane, 1,3-dimethylimidazolizinone, glymes such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, methyl salicylate, phenol and phenols, for example, alkylphenols such as methylphenol and 2,4,6-trimethylphenol as well as alkoxyphenols such as 3-methoxyphenol and 4-methoxyphenol. If necessary, they may be used in combination of two or more thereof. Dimethyl sulfoxide and sulfolane are similarly within the category of the polar solvents, but they are not used because they contain sulfur which is poisonous to the hydrogen moving catalyst.

The amount of the sulfur-free polar solvent to be used is preferably 0.1-6.0 times by weight, more preferably 0.3-3.0 times by weight as much as that of the cyclohexanone or the nucleus-substituted cyclohexanone.

It is also within the category of the present invention to use an alkaline metal compound and/or an alkaline earth metal compound as a cocatalyst. The use of the cocatalyst leads to the effect that the life of the hydrogen moving catalyst can be prolonged.

Usable examples of the alkali metal compound and/or the alkaline earth metal compound which can be added as the cocatalyst are hydroxides, carbonates, bicarbonates and the like of alkali metals and alkaline earth metals. Typical examples of these compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate and sodium hydrogen carbonate. Above all, sodium hydroxide and potassium hydroxide are preferable. These cocatalysts may be used singly or in combination of two or more thereof. The cocatalyst does not have to be added to the reaction system separately from the above-mentioned dehydrogenation catalyst. For example, after a noble metal supporting catalyst has been prepared, a salt, a hydroxide or the like of an alkali metal and/or an alkaline earth metal may be additionally supported as the alkali metal component and/or the alkaline earth metal component on the noble metal supporting catalyst, and the thus formed catalyst may be used.

The amount of the cocatalyst to be used is preferably in the range of from 2 to 30% by weight, more preferably from 5 to 20% by weight, in terms of the alkali metal and/or the alkaline earth metal, based on the weight of the catalyst metal.

It is also a preferable embodiment of the present invention to add, to the reaction using the above-mentioned cocatalyst, an organic acid in which a logarithm (pKa) of a reciprocal of an acid dissociation constant is in the range of from 3.5 to 6.0.

The preferable pKa of the organic acid is in the range of from 4.0 to 5.0. If the pKa of the organic acid is less than this range, the Schiff base is unstable, and if it is more than the above-mentioned range, the dehydrogenation reaction is impaired. Examples of the organic acid include acetic acid, propionic acid, butyric acid, isobutyric acid, valerianic acid, isovalerianic acid, hexanic acid, cyclohexanecarboxylic acid, octanoic acid, crotonic acid, vinyl acetic acid, benzoic acid, anisic acid, cinnamic acid, phenylacetic acid and 2-naphthoic acid. The amount of the organic acid to be used is preferably in the range of from 50 to 2000% by weight, more preferably from 70 to 800% by weight based on the weight of the catalyst metal.

In the case that the nitro compound is used as the hydrogen acceptor in the presence of the catalyst of a noble metal in the group VIII and the sulfur-free solvent to produce the amine and the cyclohexanone or the nucleus-substituted cyclohexanone is simultaneously reacted with the amine to prepare the aromatic secondary amino compound, the used catalyst can be recovered and then reused. In this case, if the alkali metal compound and/or the alkaline earth metal compound as the cocatalyst and the organic acid having a pKa of 3.5 to 6.0 are added to the reaction system, the amount of the catalyst to be added in each operation can be decreased as much as possible, and a reaction rate and a yield can be maintained.

It is advantageous that the reaction is carried out under the removal of water, and thus a technique is suitable in which water is removed from the reaction mixture while azeotropic distillation is done by the use of a solvent such as benzene, toluene or xylene.

The temperature at the reaction is usually in the range of from 120° to 250° C., preferably from 140° to 200° C.

In the above-mentioned reaction, when the raw materials are placed in a reactor, it is a preferable manner that the (co)catalyst, t he solvent and the amine are previously put in the reactor, stirred and then heated, and the (nucleus-substituted) cyclohexanone and the nitro compound are then simultaneously dropped into the reactor to carry out the above-mentioned reaction. Needless to say, the (nucleus-substituted) cyclohexanone and the nitro compound can be first mixed and then added to the reactor.

The mixture obtained by the above-mentioned reaction is treated in an ordinary manner such as distillation, crystallization or extraction. For example, the solution in which the reaction has already been brought to an end is filtered to separate the catalyst therefrom. The thus recovered catalyst can be reused. The resultant filtrate can be concentrated to recover the solvent. The produced aromatic secondary amino compound in the reactor can be directly used without any treatment, but if necessary, it may be purified by distillation, crystallization or the like.

According to the present invention, the desired aromatic secondary amino compound can be obtained under extremely moderate conditions and in a high yield.

Now, a method of the present invention will be described in detail in reference to examples.

EXAMPLE A1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 1.6 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 10 g of diethylene glycol dimethyl ether, 17.33 g (0.1 mol) of N-cyclohexylidene aniline and 8.29 g (0.067 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and reaction was then carried out for 4 hours by maintaining the reactor at 158°-162° C. During this reaction, water present in the catalyst and water produced by the reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 1.8 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 100%, axed the yield of diphenylamine was 87.6%.

EXAMPLES A2 to A8

Reactions were carried out by the same procedure as in Example A1 except that diethylene glycol dimethyl ether in Example A1 was replaced with various polar solvents shown in Table 1.

The results are set forth in Table 1.

                  TABLE 1                                                          ______________________________________                                                                Conversion                                                                               Yield of                                                             of Imine  Diphenylamine                                 Example                                                                               Solvent         (mol %)   (mol %)                                       ______________________________________                                         A2     N,N-dimethylacetamide                                                                          100.0     89.5                                          A3     N,N'-dimethylimida-                                                                            100.0     88.2                                                 zolidinone                                                              A4     p-cresol        99.3      84.1                                          A5     N,N-dimethylformamide                                                                          100.0     87.7                                          A6     Tetramethylurea 99.5      87.0                                          A7     N-methylpyrrolidone                                                                            98.9      83.8                                          A8     Methyl salicylate                                                                              99.8      86.5                                          ______________________________________                                    

EXAMPLE A9

Reaction was carried out by the same procedure as in Example A1 except that in place of nitrobenzene in Example A1, 23.87 g (0.202 mol) of α-methylstyrene were used as a hydrogen acceptor. As a result, the conversion of an imine was 100%, and the yield of diphenylamine was 85.9%.

COMPARATIVE EXAMPLE A1

Reaction was carried out by the same procedure as in Example A1 except that diethylene glycol dimethyl ether was not used. As a result, the conversion of an imine was 96.1%, and the yield of diphenylamine was 72.3%.

COMPARATIVE EXAMPLE A2

Reaction was carried out by the same procedure as in Example A1 except that in place of diethylene glycol dimethyl ether in Example A1, p-tert-butyltoluene was used as a solvent. As a result, the conversion of an imine was 94.0%, and the yield of diphenylamine was 72.6%.

EXAMPLE B1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 2.57 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 22.23 g of N,N-dimethylformamide, 20.5 l g (0.1 mol) of N-(4-methylcyclohexylidene)-4-methylaniline and 9.24 g (0.067 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and reaction was then carried out for 4 hours by maintaining the reactor at 138°-142° C. During this reaction, water present in the catalyst and water produced by the reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 2.9 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 100%, and the yield of 4,4'-dimethyldiphenylamine was 85.3%.

EXAMPLES B2 to B6

Reactions were carried out by the same procedure as in Example B1 except that N,N-dimethylformamide in Example B1 was replaced with various polar solvents shown in Table 2 and reaction temperature was set to 160° C.

The results are set forth in Table 2.

                  TABLE 2                                                          ______________________________________                                                               Conversion                                                                               Yield of                                                             of Imine  Ditolylamine                                   Example                                                                               Solvent        (mol %)   (mol %)                                        ______________________________________                                         B2     N,N'-dimethylimida-                                                                           99.4      94.9                                                  zolidinone                                                              B3     p-cresol       99.6      91.4                                           B4     Phenol         99.5      88.3                                           B5     Diethylene glycol                                                                             99.5      91.1                                                  dimethyl ether                                                          B6     p-methoxyphenol                                                                               99.8      93.4                                           ______________________________________                                    

EXAMPLES B7 to B14

Reactions were carried out by the same procedure as in Example B1 except that in place of the combination of N-(4-methylcyclohexylidene)-4-methylaniline and p-nitrotoluene in Example B1, combinations of various N-cyclohexylidene amino compounds and hydrogen acceptors shown in Table 3 were used. The results are set forth in Table 3.

                                      TABLE 3                                      __________________________________________________________________________          N-Cyclohexylidene-                                                                          Hydrogen                                                                               conversion                                                                           Yield                                          Example                                                                             amino compound                                                                              Acceptor                                                                               (mol %)                                                                              (mol %)                                        __________________________________________________________________________     B7   N-(4-methylcyclohexyl-                                                                      o-nitrotoluene                                                                         96.2  90.8                                                idene)-2-methylaniline                                                    B8   N-(3-ethylcyclohexyl-                                                                       p-nitrotoluene                                                                         99.1  94.2                                                idene)-4-methylaniline                                                    B9   N-(2-methylcyclohexyl-                                                                      p-nitrotoluene                                                                         100.0 96.1                                                idene)-4-methylaniline                                                    B10  N-cyclohexylidene-                                                                          m-nitrotoluene                                                                         98.9  92.1                                                3-ethylaniline                                                            B11  N-(4-methylcyclohexyl-                                                                      4-nitroanisole                                                                         99.2  93.1                                                idene)-4-methoxyaniline                                                   B12  N-(4-methylcyclohexyl-                                                                      4-nitrodiphenyl                                                                        99.3  93.2                                                idene)-4-phenoxyaniline                                                                     ether                                                        B13  N-(4-methoxycyclohexyl-                                                                     4-fluoronitro-                                                                         92.3  89.1                                                idene)-4-fluoroaniline                                                                      benzene                                                      B14  N-(4-methylcyclohexyl-                                                                      4-nitrophenol                                                                          95.6  91.1                                                idene)-4-hydroxyaniline                                                   __________________________________________________________________________

EXAMPLE B15

Reaction was carried out by the same procedure as in Example B1 except that in place of p-nitrotoluene in Example B1, 23.87 g (0.202 mol) of α-methylstyrene were used as a hydrogen acceptor. As a result, the conversion of an imine was 89.1%, and the yield of 4,4'-dimethyldiphenylamine was 82.1%.

COMPARATIVE EXAMPLE B1

Reaction was carried out by the same procedure as in Example B1 except that N,N-dimethylformamide was not used. As a result, the conversion of an imine was 51.9%, and the yield of 4,4'-dimethyldiphenylamine was 37.4%.

COMPARATIVE EXAMPLE B2

Reaction was carried out by the same procedure as in Example B1 except that in place of N,N-dimethylformamide in Example B1, p-tert-butyltoluene was used as a solvent. As a result, the conversion of an imine was 49.1%, and the yield of 4,4'-dimethyldiphenylamine was 35.3%.

COMPARATIVE EXAMPLE B3

Reaction was carried out by the same procedure as in Example B7 except that N,N-dimethylformamide was not used. As a result, the conversion of an imine was 31.3%, and the yield of 4,2'-dimethyldiphenylamine was 15.5%.

COMPARATIVE EXAMPLE B4

Reaction was carried out by the same procedure as in Example B9 except that N,N-dimethylformamide was not used. As a result, the conversion of an imine was 12.1%, and the yield of 2,4'-dimethyldiphenylamine was 4.3%.

EXAMPLE C1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 3.72 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd. and 20 g of diethylene glycol dimethyl ether, and in the dropping device was prepared a mixed solution of 34.66 g (0.2 mol) of N-cyclohexylidene aniline and 16.58 g (0.13 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 4 hours, while a temperature of 158°-162° C. was maintained. After completion of the dropping, the solution was stirred for 0.5 hour, while this temperature range was maintained. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 4.8 g. Next, the reaction solution in the reactor was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 100%, and the yield of diphenylamine was 98.5%.

EXAMPLES C2 to C8

Reactions were carried out by the same procedure as in Example C1 except that diethylene glycol dimethyl ether in Example C1 was replaced with various polar solvents shown in Table 4.

The results are set forth in Table 4.

COMPARATIVE EXAMPLE C1

Reaction was carried out by the same procedure as in Example C1 except that in place of diethylene glycol dimethyl ether in Example C1, p-tert-butyltoluene was used as a solvent. As a result, the conversion of an imine was 35.0%, and the selectivity of diphenylamine was 90.2%.

                  TABLE 4                                                          ______________________________________                                                                Conversion                                                                               Yield of                                                             of Imine  Diphenylamine                                 Example                                                                               Solvent         (mol %)   (mol %)                                       ______________________________________                                         C2     Diethylene glycol                                                                              100.0     98.4                                                 diethyl ether                                                           C3     N,N'-dimethylimida-                                                                            100.0     98.5                                                 zolidinone                                                              C4     N,N-dimethylformamide                                                                          100.0     98.7                                          C5     N,N-dimethylacetamide                                                                          100.0     99.0                                          C6     Tetramethylurea 99.0      97.0                                          C7     N-methylpyrrolidone                                                                            91.0      89.3                                          C8     Methyl salicylate                                                                              97.0      95.0                                          C9     p-cresol        98.0      96.5                                          ______________________________________                                    

EXAMPLE D1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 2.57 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd. and 22.23 g of N,N-dimethylformamide, and in the dropping device was prepared and stored a mixed solution of 20.51 g (0.1 mol) of N-(4-methylcyclohexylidene) 4-methylaniline and 9.24 g (0.067 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 4 hours, while a temperature of 138°-142° C. was maintained. After completion of the dropping, the solution was stirred for 1 hour, while this temperature range was maintained. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 4.0 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 98.6%, and the yield of 4,4'-dimethyldiphenylamine was 93.5%.

EXAMPLES D2 to D6

Reactions were carried out by the same procedure as in Example D1 except that N,N-dimethylformamide in Example D1 was replaced with various polar solvents shown in Table 5 and reaction temperature was set to 160° C.

The results are set forth in Table 5.

                  TABLE 5                                                          ______________________________________                                                               Conversion                                                                               Yield of                                                             of Imine  Ditolylamine                                   Example                                                                               Solvent        (mol %)   (mol %)                                        ______________________________________                                         D2     N,N'-dimethylimida-                                                                           98.2      96.3                                                  zolidinone                                                              D3     p-cresol       99.1      94.1                                           D4     Phenol         99.0      93.4                                           D5     Diethylene glycol                                                                             98.3      95.2                                                  dimethyl ether                                                          D6     p-methoxyphenol                                                                               99.2      95.3                                           ______________________________________                                    

EXAMPLES D7 to D14

Reactions were carried out by the same procedure as in Example D1 except that the combination of N-cyclohexylidene amino compound and a hydrogen acceptor in Example D1 was changed to combinations shown in Table 6.

The results are set forth in Table 6.

                                      TABLE 6                                      __________________________________________________________________________          N-Cyclohexylidene-                                                                          Hydrogen                                                                               Conversion                                                                           Yield                                          Example                                                                             amino Compound                                                                              Acceptor                                                                               (mol %)                                                                              (mol %)                                        __________________________________________________________________________     D7   N-(4-methylcyclohexyl-                                                                      o-nitrotoluene                                                                         96.1  94.4                                                idene)-2-methylaniline                                                    D8   N-(3-ethylcyclohexyl-                                                                       p-nitrotoluene                                                                         98.1  96.5                                                idene)-4-methylaniline                                                    D9   N-(2-methylcyclohexyl-                                                                      P-nitrotoluene                                                                         99.7  98.5                                                idene)-4-methylaniline                                                    D10  N-cyclohexylidene-                                                                          m-nitrotoluene                                                                         98.8  95.9                                                3-ethylaniline                                                            D11  N-(4-methylcyclohexyl-                                                                      4-nitroanisole                                                                         98.1  94.9                                                idene)-4-methoxyaniline                                                   D12  N-(4-methylcyclohexyl-                                                                      4-nitrodiphenyl                                                                        98.2  95.3                                                idene)-4-phenoxyaniline                                                                     ether                                                        D13  N-(4-methoxycyclohexyl-                                                                     4-fluoronitro-                                                                         90.6  89.1                                                idene)-4-fluoroaniline                                                                      benzene                                                      D14  N-(4-methylcyclohexyl-                                                                      4-nitrophenol                                                                          96.0  93.7                                                idene)-4-hydroxyaniline                                                   __________________________________________________________________________

EXAMPLE E1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 1.86 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 0.24 g of 1N-NaOH, 10 g of diethylene glycol dimethyl ether, 17.33 g (0.1 mol) of N-cyclohexylidene aniline and 8.29 g (0.067 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and reaction was then carried out for 2 hours by maintaining the reactor at 158°-162° C. During this reaction, water present in the catalyst and water produced by the reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 2.6 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 100%, and the yield of diphenylamine was 93.0%.

EXAMPLES E2 TO E8 AND COMPARATIVE EXAMPLES E1 TO E3

Reactions were carried out by the same procedure as in Example E1 except that at diethylene glycol dimethyl ether in Example E1 was replaced with various polar solvents shown in Table 7.

The results are set forth in Table 7.

                                      TABLE 7                                      __________________________________________________________________________                               Conversion                                                                           Yield of                                                                 of Imine                                                                             Diphenylamine                                  Example Solvent     Cocatalyst                                                                           (mol %)                                                                              (mol %)                                        __________________________________________________________________________     E2      N,N-dimethylacetamide                                                                      NaOH  100.0 94.2                                           E3      N,N'-dimethylimida-                                                                        NaOH  100.0 93.5                                                   zolidinone                                                             E4      p-cresol    NaOH  98.8  90.4                                           E5      N,N-dimethylformamide                                                                      NaOH  100.0 92.8                                           E6      Tetramethylurea                                                                            NaOH  99.2  90.6                                           E7      N-methylpyrrolidone                                                                        NaOH  98.4  89.7                                           E8      Methyl salicylate                                                                          NaOH  99.6  92.2                                           Comp. Ex. E1                                                                           --          NaOH  97.5  84.8                                           Comp. Ex. E2                                                                           --          --    92.5  68.1                                           Comp. Ex. E3                                                                           p-tert-butyltoluene                                                                        NaOH  91.1  67.4                                           __________________________________________________________________________

EXAMPLES E9 and E10

Reactions were carried out by the same procedure as in Example E1 except that in place of 0.24 g of 1N-NaOH in Example E1, an alkali metal compound and/or an alkaline earth metal compound shown in Table 8 was used as a co-catalyst.

The results are set forth together with those of Example E1 in Table 8.

                  TABLE 8                                                          ______________________________________                                         Cocatalyst         Conversion                                                                               Yield of                                                           Amount*   of Imine                                                                               Diphenylamine                               Example                                                                               Kind      (wt %/Pd) (mol %) (mol %)                                     ______________________________________                                         E1     NaOH      Na: 11.9  100.0   93.0                                        E9     Ca(OH).sub.2                                                                             Ca: 20    100.0   92.3                                        E10    NaOH +    Na: 5     100.0   93.0                                               Mg(OH).sub.2                                                                             Mg: 12                                                        ______________________________________                                          *The amount of the cocatalyst in terms of an alkali metal and/or an            alkaline earth metal.                                                    

EXAMPLE F1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 2.57g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 0.30 g of 1N-NaOH, 22.23 g of N,N-dimethylformamide, 20.51 g (0.1 mol) of N-(4-methylcyclohexylidene)-4-methylaniline and 9.24 g (0.067 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and reaction was then carried out for 2 hours by maintaining the reactor at 138°-142° C. During this reaction, water present in the catalyst and water produced by the reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 3.6 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 99.7%, and the yield of 4,4'-dimethyldiphenylamine was 90.9%.

COMPARATIVE EXAMPLE F1

Reaction was carried out by the same procedure as in Example F1 except that N,N-dimethylformamide was not used. As a results, the conversion of an imine was 46.6%, and the yield of 4,4'-dimethyldiphenylamine was 36.0%.

COMPARATIVE EXAMPLE F2

Reaction was carried out by the same procedure as in Example F1 except that 1N-NaOH and N,N-dimethylformamide were not used. As a result, the conversion of an imine was 45.3%, and the yield of 4,4'-dimethyldiphenylamine was 31.5%.

EXAMPLES F2 TO F6

Reactions were carried out by the same procedure as in Example F1 except that N,N-dimethylformamide in Example F1 was replaced with various polar solvents shown in Table 9 and reaction temperature was set to 160° C.

The results are set forth in Table 9.

                  TABLE 9                                                          ______________________________________                                                               Conversion                                                                               Yield of                                                             of Imine  Ditolylamine                                   Example                                                                               Solvent        (mol %)   (mol %)                                        ______________________________________                                         F2     N,N'-dimethylimida-                                                                           98.5      95.2                                                  zolidinone                                                              F3     p-cresol       100.0     94.6                                           F4     Phenol         99.3      90.6                                           F5     Diethylene glycol                                                                             98.7      93.1                                                  dimethyl ether                                                          F6     p-methoxyphenol                                                                               98.8      94.1                                           ______________________________________                                    

EXAMPLES F7AND F8

Reactions were carried out by the same procedure as in Example F1 except that in place of 0.3 g of 1N-NaOH in Example F1, an alkaline metal compound and/or an alkaline earth metal compound shown in Table 10 was used as a co-catalyst.

The results are set forth together with those of Example F1 in Table 10.

                  TABLE 10                                                         ______________________________________                                         Cocatalyst         Conversion                                                                               Yield of                                                           Amount*   of Imine                                                                               Diphenylamine                               Example                                                                               Kind      (wt %/Pd) (mol %) (mol %)                                     ______________________________________                                         F1     NaOH      Na: 10.7  99.7    90.9                                        F7     Ca(OH).sub.2                                                                             Ca: 20    99.7    89.8                                        F8     NaOH +    Na: 5     100.0   90.6                                               Mg(OH).sub.2                                                                             Mg: 12                                                        ______________________________________                                          *The amount of the cocatalyst in terms of an alkali metal and/or an            alkaline earth metal.                                                    

EXAMPLES F9 TO F16

Reactions were carried out by the same procedure as in Example F1 except that the combination of N-(4-methylcyclohexylidene)-4-methylaniline and p-nitrotoluene in Example F1 was changed to combinations of N-cyclohexylidene amino compounds and hydrogen acceptors shown in Table 11.

The results are set forth in Table 11.

                                      TABLE 11                                     __________________________________________________________________________          N-Cyclohexylidene-                                                                          Hydrogen                                                                               Conversion                                                                           Yield                                          Example                                                                             amino Compound                                                                              Acceptor                                                                               (mol %)                                                                              (mol %)                                        __________________________________________________________________________     F9   N-(4-methylcyclohexyl-                                                                      o-nitrotoluene                                                                         97.9  94.0                                                idene)-2-methylaniline                                                    F10  N-(3-ethylcyclohexyl-                                                                       p-nitrotoluene                                                                         98.3  95.2                                                idene)-4-methylaniline                                                    F11  N-(2-methylcyclohexyl-                                                                      p-nitrotoluene                                                                         99.8  97.1                                                idene)-4-methylaniline                                                    F12  N-cyclohexylidene-                                                                          m-nitrotoluene                                                                         99.1  94.7                                                3-ethylaniline                                                            F13  N-(4-methylcyclohexyl-                                                                      4-nitroanisole                                                                         98.5  93.5                                                idene)-4-methoxyaniline                                                   F14  N-(4-methylcyclohexyl-                                                                      4-nitrodiphenyl                                                                        98.5  93.6                                                idene)-4-phenoxyaniline                                                                     ether                                                        F15  N-(4-methoxycyclohexyl-                                                                     4-fluoronitro-                                                                         90.8  88.3                                                idene)-4-fluoroaniline                                                                      benzene                                                      F16  N-(4-methylcyclohexyl-                                                                      4-nitrophenol                                                                          96.2  92.8                                                idene)-4-hydroxyaniline                                                   __________________________________________________________________________

COMPARATIVE EXAMPLE F3

Reaction was carried out by the same procedure as in Example F9 except that N,N-dimethylformamide in Example F9 was not used. As a result, the conversion of an imine was 55.2%, and the yield of 4,2'-dimethyldiphenylamine was 42.3%.

COMPARATIVE EXAMPLE F4

Reaction was carried out by the same procedure as in Example F9 except that 1N-NaOH and N,N-dimethylformamide in Example F9 were not used. As a result, the conversion of an imine was 17.0%, and the yield of 4,2'-dimethyldiphenylamine was 12.5%.

COMPARATIVE EXAMPLE F5

Reaction was carried out by the same procedure as in Example F11 except that N,N-dimethylformamide in Example F11 was not used. As a result, the conversion of an imine was 48.2%, and the yield of 2,4'-dimethyldiphenylamine was 35.8%.

COMPARATIVE EXAMPLE F6

Reaction was carried out by the same procedure as in Example F11 except that 1N-NaOH and N,N-dimethylformamide in Example F11 were not used. As a result, the conversion of an imine was 11.3%, and the yield of 2,4'-dimethyldiphenylamine was 3.5%.

EXAMPLE G1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 1.86 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co.. Ltd., 0.24 g of 1N-NaOH, 17.33 g (0.1 mol) of N-cyclohexylideneaniline, 8.29 g (0.067 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and reaction was then carried out for 3 hours by maintaining the reactor at 158°-162° C. During this reaction, water present in the catalyst and water produced by the reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser and then separating it by the separator The amount of the removed water was 2.7 g. Next, the reaction solution was cooled to room temperature and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 99.4%, and the yield of diphenylamine was 86.7%.

EXAMPLES G2 TO G10 AND COMPARATIVE EXAMPLE G1

Reactions were carried out by the same procedure as in Example G1 except that in place of 0.24 g of 1N-NaOH in Example G1, various kinds of catalysts were used in various amounts as shown in Table 12.

The results are set forth together with those of Example G1 in Table 12.

                                      TABLE 12                                     __________________________________________________________________________     Example/                                                                              Cocatalyst      Conversion                                                                           Yield of                                          Comp.            Amount*                                                                              of Imine                                                                             Diphenylamine                                     Example                                                                               Kind      (wt %/Pd)                                                                            (mol %)                                                                              (mol %)                                           __________________________________________________________________________     Example G1                                                                            NaOH      11.9  99.4  86.7                                              Example G2                                                                            NaOH      20    100.0 87.5                                              Example G3                                                                            Na.sub.2 CO.sub.3                                                                        12    99.8  86.9                                              Example G4                                                                            NaHCO.sub.3                                                                              12    99.0  86.0                                              Example G5                                                                            KOH       6     100.0 87.6                                              Example G6                                                                            LiOH      5     98.5  84.5                                              Example G7                                                                            Ca(OH).sub.2                                                                             20    97.7  83.9                                              Example G8                                                                            Mg(OH).sub.2                                                                             12    98.7  84.8                                              Example G9                                                                            NaOH + Ca(OH).sub.2                                                                      Na: 10                                                                               99.2  85.9                                                               Ca: 10                                                        Example G10                                                                           KOH + Mg(OH).sub.2                                                                       K: 5  99.7  86.5                                                               Mg: 12                                                        Comp.  --        --    90.1  69.2                                              Example G1                                                                     __________________________________________________________________________      *The amount of the cocatalyst in terms of an alkali metal and/or an            alkaline earth metal.                                                    

EXAMPLE H1

In a 100 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 2.57 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 0.30 g of 1N-NaOH, 20.51 g (0.1 mol) of N-(4-methylcyclohexylidene)-4methylaniline and 9.24 g (0.067 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 160° C. with stirring, and reaction was the carried out for 3 hours by maintaining the reactor at 158°-162° C. During this reaction, water present in the catalyst and water produced by the reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 3.0 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of an imine was 98.2%, and the yield of 4,4'-dimethyldiphenylamine was 85.5%.

EXAMPLES H2 TO H6

Reactions were carried out by the same procedure as in Example H1 except that in place of a cocatalyst in Example H1, various kinds of cocatalysts were used in various amounts as shown in Table 13.

The results are set forth together with those of Example H1 in Table 13.

                  TABLE 13                                                         ______________________________________                                         Cocatalyst         Conversion                                                                               Yield of                                                           Amount*   of Imine                                                                               Diphenylamine                               Example                                                                               Kind      (wt %/Pd) (mol %) (mol %)                                     ______________________________________                                         H1     NaOH      10.7      98.2    85.5                                        H2     NaOH      20        98.6    86.7                                        H3     NaOH      5         97.2    83.5                                        H4     NaHCO.sub.3                                                                              12        98.2    85.1                                        H5     Ca(OH).sub.2                                                                             20        96.8    82.8                                        H6     NaOH +    Na: 10    98.7    84.7                                               Ca(OH).sub.2                                                                             Mg: 10                                                        ______________________________________                                          *The amount of the cocatalyst in terms of an alkali metal and/or an            alkaline earth metal.                                                    

EXAMPLES H7TO H14

Reactions were carried out by the same procedure as in Example H1 except that the combination of an N-cyclohexylidene amino compound and a hydrogen acceptor in Example H1 was changed to combinations shown in Table 14.

The results are set forth in Table 14.

                                      TABLE 14                                     __________________________________________________________________________          N-Cyclohexylidene-                                                                          Hydrogen                                                                               Conversion                                                                           Yield                                          Example                                                                             amino Compound                                                                              Acceptor                                                                               (mol %)                                                                              (mol %)                                        __________________________________________________________________________     H7   N-(4-methylcyclohexyl-                                                                      o-nitrotoluene                                                                         95.2  85.3                                                idene)-2-methylaniline                                                    H8   N-(3-ethylcyclohexyl-                                                                       p-nitrotoluene                                                                         98.3  88.6                                                idene)-4-methylaniline                                                    H9   N-(2-methylcyclohexyl-                                                                      p-nitrotoluene                                                                         99.1  90.3                                                idene)-4-methylaniline                                                    H10  N-cyclohexylidene-                                                                          m-nitrotoluene                                                                         97.6  86.3                                                3-ethylaniline                                                            H11  N-(4-methylcyclohexyl-                                                                      4-nitroanisole                                                                         97.9  87.2                                                idene)-4-methoxyaniline                                                   H12  N-(4-methylcyclohexyl-                                                                      4-nitrodiphenyl                                                                        98.1  87.0                                                idene)-4-phenoxyaniline                                                                     ether                                                        H13  N-(4-methoxycyclohexyl-                                                                     4-fluoronitro-                                                                         89.8  81.9                                                idene)-4-fluoroaniline                                                                      benzene                                                      H14  N-(4-methylcyclohexyl-                                                                      4-nitrophenol                                                                          91.2  82.6                                                idene)-4-hydroxyaniline                                                   __________________________________________________________________________

COMPARATIVE EXAMPLE H1

Reaction was carried out by the same procedure as Example H1 except that 1N-NaOH was not used. As a result, the conversion of an imine was 79.9%, and the yield of 4,4'-dimethyldiphenylamine was 66.8%.

COMPARATIVE EXAMPLE H2

Reaction was carried out by the same procedure as Example H7 except that 1N-NaOH was not used. As a result, the conversion of an imine was 61.3%, and the yield of 4,2'-dimethyldiphenylamine was 35.3%.

COMPARATIVE EXAMPLE H3

Reaction was carried out by the same procedure as Example H9 except that 1N-NaOH was not used. As a result, the conversion of an imine was 55.9%, and the yield of 4,2'-dimethyldiphenylamine was 34.1%.

EXAMPLE I1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 5.59 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 25.68 g of diethylene glycol dimethyl ether, 13.97 g (0.15 mol) of aniline, 29.44 g (0.3 mol) of cyclohexanone and 24.87 g (0.2 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and reaction was then carried out for 3 hours by maintaining the reactor at 158°-162° C. Water present in the catalyst and water produced during this reaction was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 12.4 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of cyclohexanone was 100%, and the yield of diphenylamine was 86.8%.

EXAMPLE I2 to I8

Reactions were carried out by the same procedure as in Example I1 except that diethylene glycol dimethyl ether in Example I1 was replaced with various polar solvents shown in Table 15.

The results are set forth in Table 15.

                  TABLE 15                                                         ______________________________________                                                                Conversion                                                                               Yield of                                                             of Imine  Diphenylamine                                 Example                                                                               Solvent         (mol %)   (mol %)                                       ______________________________________                                         I2     N,N-dimethylacetamide                                                                          100.0     90.2                                          I3     N,N'-dimethylimida-                                                                            98.9      86.2                                                 zolidinone                                                              I4     p-cresol        100.0     91.7                                          I5     N,N-dimethylformamide                                                                          100.0     91.4                                          I6     Tetramethylurea 98.2      87.4                                          I7     N-methylpyrrolidone                                                                            97.4      85.8                                          ______________________________________                                    

COMPARATIVE EXAMPLE I1

Reaction was carried out by the same procedure as in Example I1 except that diethylene glycol dimethyl ether was not used. As a result, the conversion of cyclohexanone was 96.6%, and the yield of diphenylamine was 76.3%.

COMPARATIVE EXAMPLE I2

Reaction was carried out by the same procedure as in Example I1 except that in place of diethylene glycol dimethyl ether, p-tert-butyltoluene was used as a solvent. As a result, the conversion of cyclohexanone was 91.1%, and the yield of diphenylamine was 67.3%.

EXAMPLE I8

Reaction was carried out by the same procedure as in Example I1 except that 32.39 g (0.39 mol) of cyclohexanone, 9.31 g (0.1 mol) of aniline and 24.62 g (0.2 mol) nitrobenzene were used. As a result, the yield of diphenylamine was 89.5%, and 1.8% of triphenylamine and 2.9% of N-cyclohexylaniline were produced.

EXAMPLE J1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 7.72 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 60.00 g of N,N-dimethylformamide, 16.07 g (0.15 mol) of p-toluidine, 33.65 g (0.3 mol) of 4-methylcyclohexanone and 27.43 g (0.2 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and reaction was then carried out for 3 hours by maintaining the reactor at 134°-142° C. Water present in the catalyst and water produced during this reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 12.34 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of 4-methylcyclohexanone was 98.6%, and the yield of ditolylamine was 91.6%.

EXAMPLES J2 TO J7

Reactions were carried out by the same procedure as in Example J1 except that N,N-dimethylformamide in Example J1 was replaced with various polar solvents shown in Table 16 and reaction temperature was set to 160° C.

The results are set forth in Table 16.

                  TABLE 16                                                         ______________________________________                                                                          Yield of                                                             Conversion                                                                               Ditolylamine                                  Example                                                                               Solvent         (mol %)   (mol %)                                       ______________________________________                                         J2     N,N-dimethylacetamide                                                                          99.8      90.2                                          J3     N,N'-dimethylimida-                                                                            98.9      89.2                                                 zolidinone                                                              J4     p-cresol        100.0     94.3                                          J5     Diethylene glycol                                                                              98.0      89.4                                                 dimethyl ether                                                          J6     Tetramethylurea 98.7      87.9                                          J7     N-methylpyrrolidone                                                                            97.4      88.8                                          ______________________________________                                    

COMPARATIVE EXAMPLE J1

Reaction was carried out by the same procedure as in Example J1 except that N,N-dimethylformamide was not used. As a result, the conversion of 4-methylcyclohexanone was 51.6%, and the yield of ditolylamine was 7.9%.

COMPARATIVE EXAMPLE J2

Reaction was carried out by the same procedure as in Example J1 except that in place of N,N-dimethylformamide in Example J1, xylene was used as a solvent. As a result, the conversion of p-methylcyclohexanone was 53.7%, and the yield of ditolylamine was 9.0%.

EXAMPLES J8 TO J13

Reaction was carried out by the same procedure as in Example J1 except that the combination of p-toluidine, 4-methylcyclohexanone and p-nitrotoluene was replaced with materials shown in Table 17.

The results are set forth in Table 17.

                                      TABLE 17                                     __________________________________________________________________________        Cyclohexanone                                                               Ex-                                                                               (nucleus-                                         Conver-                   am-                                                                               substitured           Nitro-       Desired        sion Yield                ple                                                                               compound)                                                                               Amine        Compound     Compound       (mol                                                                                (mol                 __________________________________________________________________________                                                               %)                   J8                                                                                 ##STR5##                                                                                ##STR6##                                                                                    ##STR7##                                                                                    ##STR8##      97.1 90.7                 J9                                                                                 ##STR9##                                                                                ##STR10##                                                                                   ##STR11##                                                                                   ##STR12##     100.0                                                                               89.1                 J10                                                                                ##STR13##                                                                               ##STR14##                                                                                   ##STR15##                                                                                   ##STR16##     99.5 87.1                 J11                                                                                ##STR17##                                                                               ##STR18##                                                                                   ##STR19##                                                                                   ##STR20##     99.6 90.0                 J12                                                                                ##STR21##                                                                               ##STR22##                                                                                   ##STR23##                                                                                   ##STR24##     98.1 89.5                 J13                                                                                ##STR25##                                                                               ##STR26##                                                                                   ##STR27##                                                                                   ##STR28##     98.9 88.9                 __________________________________________________________________________

EXAMPLE K1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 5.59 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 25.68 g of diethylene glycol dimethyl ether and 13.97 g (0.15 mol) of aniline, and in the dropping device was prepared and stored a mixed solution of 29.44 g (0.3 mol) of cyclohexanone and 24.87 g (0.2 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 4 hours, while a temperature of 158°-162° C. was maintained. After completion of the dropping, the solution was stirred for 0.5 hour, while this temperature range was maintained. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 12.6 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of cyclohexanone was 100%. and the yield of diphenylamine was 99.2%.

EXAMPLES K2 to K8

Reactions were carried out by the same procedure as in Example K1 except that diethylene glycol dimethyl ether in Example K1 was replaced with various polar solvents shown in Table 18.

The results are set forth in Table 18.

                  TABLE 18                                                         ______________________________________                                                                          Yield of                                                             Conversion                                                                               Diphenylamine                                 Example                                                                               Solvent         (mol %)   (mol %)                                       ______________________________________                                         K2     N,N-dimethylacetamide                                                                          100.0     98.8                                          K3     N,N'-dimethylimida-                                                                            100.0     98.5                                                 zolidinone                                                              K4     p-cresol        98.9      97.1                                          K5     N,N-dimethylformamide                                                                          100.0     99.1                                          K6     Tetramethylurea 99.5      98.0                                          K7     N-methylpyrrolidone                                                                            96.8      94.9                                          K8     Methyl salicylate                                                                              98.7      96.8                                          ______________________________________                                    

COMPARATIVE EXAMPLE K1

Reaction was carried out by the same procedure as in Example K1 except that in place of diethylene glycol dimethyl ether in Example K1, p-tert-butyltoluene was used as a solvent. As a result, the conversion of cyclohexanone was 77.5%, and the yield of diphenylamine was 48.5%.

EXAMPLE L1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 7.72 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 60.00 g of N,N-dimethylformamide and 16.07 g (0.15 mol) of p-toluidine, and in the dropping device was prepared and stored a mixed solution of 33.65 g (0.3 mol) of 4-methylcyclohexanone and 27.43 g (0.2 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 6 hours, while a temperature of 134°-142° C. was maintained. After completion of the dropping, the solution was stirred for 1 hour, while this temperature range was kept up. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 12.5 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of 4-methylcyclohexanone was 99.6%, and the yield of ditolylamine was 97.7%.

EXAMPLES L2 TO L7

Reactions were carried out by the same procedure as in Example L1 except that N,N-dimethylformamide in Example L1 was replaced with various polar solvents shown in Table 19 and reaction temperature was set to 160° C.

The results are set forth in Table 19.

                  TABLE 19                                                         ______________________________________                                                                          Yield of                                                             Conversion                                                                               Ditolylamine                                  Example                                                                               Solvent         (mol %)   (mol %)                                       ______________________________________                                         L2     N,N-dimethylacetamide                                                                          99.7      97.1                                          L3     N,N'-dimethylimida-                                                                            99.1      96.5                                                 zolidinone                                                              L4     p-cresol        99.9      98.1                                          L5     Diethylene glycol                                                                              98.0      96.1                                                 dimethyl ether                                                          L6     Tetramethylurea 99.2      97.1                                          L7     N-methylpyrrolidone                                                                            98.7      96.9                                          ______________________________________                                    

EXAMPLES L8 TO L13

Reactions were carried out by the same procedure as in Example L1 except that p-toluidine, 4-methylcyclohexanone and p-nitrotoluene in Example L1 were replaced with various materials shown in Table 20.

The results are set forth in Table 20.

                                      TABLE 20                                     __________________________________________________________________________        Cyclohexanone                                                               Ex-                                                                               (nucleus-                                         Conver-                   am-                                                                               substitured           Nitro-       Desired        sion Yield                ple                                                                               compound)                                                                               Amine        Compound     Compound       (mol                                                                                (mol                 __________________________________________________________________________                                                               %)                   L8                                                                                 ##STR29##                                                                               ##STR30##                                                                                   ##STR31##                                                                                   ##STR32##     98.2 95.1                 L9                                                                                 ##STR33##                                                                               ##STR34##                                                                                   ##STR35##                                                                                   ##STR36##     99.8 97.8                 L10                                                                                ##STR37##                                                                               ##STR38##                                                                                   ##STR39##                                                                                   ##STR40##     99.6 96.8                 L11                                                                                ##STR41##                                                                               ##STR42##                                                                                   ##STR43##                                                                                   ##STR44##     99.8 98.8                 L12                                                                                ##STR45##                                                                               ##STR46##                                                                                   ##STR47##                                                                                   ##STR48##     98.9 96.7                 L13                                                                                ##STR49##                                                                               ##STR50##                                                                                   ##STR51##                                                                                   ##STR52##     99.3 96.9                 __________________________________________________________________________

EXAMPLE M1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer and a stirrer were placed 7.72 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 0.91 g of 1N-NaOH (Na content=10.8 wt %/Pd), 60.00 of N,N-dimethylformamide, 16.07 g (0.15 mol) of p-toluidine, 33.65 g (0.3 mol) of 4-methylcyclohexanone and 27.43 g (0.2 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and reaction was then carried out for 3 hours by maintaining the reactor at 138°-142° C. Water present in the catalyst and water produced during this reaction were removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 15.22 g. Next, the reaction solution was cooled to room temperature, and the 5 % Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of 4-methylcyclohexanone was 99.8%, and the yield of ditolylamine was 94.2%.

EXAMPLE

In a 300 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 4.66 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 1.21 g of 1N-NaOH, 0.33 g of butyric acid, 42.80 g of diethylene glycol dimethyl ether and 23.28 g (0.25 mol) of aniline, and in the dropping device was prepared and stored a mixed solution of 49.07 g (0.5 mol) of cyclohexanone and 41.45 g (0.33 mol) of nitrobenzene. The reactor was heated to 160° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 4 hours, while a temperature of 158°-162° C. was maintained. After completion of the dropping, the solution was stirred for 0.5 hour, while this temperature range was kept up. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 21.0 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of cyclohexanone was 100%, and the yield of diphenylamine was 99.9%.

In succession, the previously recovered catalyst was used, and 5% Pd/C containing 50% of water, NaOH and butyric acid were added as shown in Table 21 and reaction was then similarly carried out. As a result, the average amount of the added new 5% Pd/C catalyst necessary to maintain a reaction rate and a selectivity was about 3% of its initial amount.

                                      TABLE 21                                     __________________________________________________________________________           Amount of Added                                                                               Butyric                                                   Number of                                                                            New Catalyst                                                                            1N-NaOH                                                                              Acid                                                                               Conversion                                                                           Selectivity                                     Recycling                                                                            5% Pd/C (g)                                                                             (g)   (g) (mol %)                                                                              (mol %)                                         __________________________________________________________________________     1     --       --    0.33                                                                               100.0 99.8                                            2     --       --    0.33                                                                               100.0 99.7                                            3     --       --    0.33                                                                               100.0 99.7                                            4     --       --    0.33                                                                               100.0 99.1                                            5     0.70     0.18  0.33                                                                               100.0 99.7                                            6     --       --    0.33                                                                               99.7  98.6                                            7     0.47     0.12  0.33                                                                               100.0 99.5                                            8     --       --    0.33                                                                               100.0 99.0                                            9     --       --    0.33                                                                               98.7  97.3                                            10    0.23     0.06  0.33                                                                               100.0 99.3                                            __________________________________________________________________________

EXAMPLE M3

In a 300 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 4.66 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 42.80 g of diethylene glycol dimethyl ether and 23.28 g (0.25 mol) of aniline, and in the dropping device was prepared and stored a mixed solution of 49.07 g (0.5 mol) of cyclohexanone and 41.45 g (0.33 mol) of nitrobenzene. Afterward, the reactor was heated up to 160° C. with stirring, and after the removal of water present in the catalyst, the solution ill the dropping device was dropped over 4 hours, while a temperature of 158°-162° C. was maintained. After completion of the dropping, the solution was stirred for 0.5 hour, while this temperature range was maintained. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 21.0 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of cyclohexanone was 100%, and the yield of diphenylamine was 99.2% .

In succession, the previously recovered catalyst was used, and 5% Pd/C was added as shown in Table 22 and the reaction was then similarly carried out. As a result, the average amount of the added new 5% Pd/C catalyst necessary to maintain a reaction rate and a selectivity was about 15% of its initial amount.

                  TABLE 22                                                         ______________________________________                                                  Amount of Added                                                       Number of                                                                               New 5% Pd/C   Conversion Selectivity                                  Recycling                                                                               Catalyst (g)  (mol %)    (mol %)                                      ______________________________________                                         1        0.47          98.7       96.7                                         2        0.47          94.5       92.4                                         3        0.93          95.7       93.3                                         4        0.93          96.0       93.7                                         5        0.93          96.2       94.0                                         6        0.47          93.6       90.8                                         7        0.70          95.3       92.6                                         8        0.70          94.1       91.7                                         9        0.70          93.4       91.2                                         10       0.70          92.7       90.4                                         ______________________________________                                    

EXAMPLE N1

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 7.72 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 0.91 g of 1N-NaOH, 0.55 g of butyric acid, 60.00 g of N,N-dimethylformamide and 16.07 g (0.15 mol) of toluidine, and in the dropping device was prepared and stored a mixed solution of 33.65 g (0.3 mol) of 4-methylcyclohexanone and 27.43 g (0.2 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 6 hours, while a temperature of 134°-142° C. was maintained. After completion of the dropping, the solution was stirred for 1 hour, while this temperature range was maintained. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 12.6 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of 4-methylcyclohexanone was 99.8%, and the yield of ditolylamine was 98.8%.

In succession, the previously recovered catalyst was used, and 5% Pd/C containing 50% of water, NaOH and butyric acid were added as shown in Table 23 and the reaction was then similarly carried out. As a result, the average amount of the added new catalyst necessary to maintain a reaction rate and a selectivity was about 6.0% of its initial amount.

                                      TABLE 23                                     __________________________________________________________________________           Amount of Added                                                                               Butyric                                                   Number of                                                                            New Catalyst                                                                            1N-NaOH                                                                              Acid                                                                               Conversion                                                                           Selectivity                                     Recycling                                                                            5% Pd/C (g)                                                                             (g)   (g) (mol %)                                                                              (mol %)                                         __________________________________________________________________________     1     0.39     0.08  0.55                                                                               100.0 99.2                                            2     0.19     0.08  0.55                                                                               100.0 99.1                                            3     0.19     0.08  0.55                                                                               100.0 99.0                                            4     0.19     0.08  0.55                                                                               100.0 99.1                                            5     0.19     0.08  0.55                                                                               100.0 98.9                                            __________________________________________________________________________

EXAMPLE N2

In a 200 ml round bottom flask equipped with a reflux condenser with a separator, a thermometer, a dropping device and a stirrer were placed 7.72 g of 5% Pd/C containing 50% of water made by N. E. Chemcat Co., Ltd., 60.00 g of N,N-dimethylformamide and 16.07 g (0.15 mol) of toluidine, and in the dropping device was prepared and stored a mixed solution of 33.65 g (0.3 mol) of 4-methylcyclohexanone and 27.43 g (0.2 mol) of p-nitrotoluene. Afterward, the reactor was heated up to 140° C. with stirring, and after the removal of water present in the catalyst, the solution in the dropping device was dropped over 6 hours, while a temperature of 134°-142° C. was maintained. After completion of the dropping, the solution was stirred for 1 hour, while this temperature range was maintained. Water produced during this step was removed from the reaction system by adding benzene to the reactor to cause azeotropy, condensing water by the reflux condenser, and then separating it by the separator. The amount of the removed water was 12.5 g. Next, the reaction solution was cooled to room temperature, and the 5% Pd/C was then removed from the reaction solution by filtration. The resultant filtrate was analyzed by the use of gas chromatography. The conversion of 4-methylcyclohexanone was 99.6%, and the yield of ditolylamine was 98.7%.

In succession, the previously recovered catalyst was used, and the new catalyst was added as much as an average amount of about 8.3% based on the initial amount as shown in Table 24 and the reaction was then similarly carried out. The results obtained were shown in the same table.

                  TABLE 24                                                         ______________________________________                                                  Amount of Added                                                       Number of                                                                               New 5% Pd/C   Conversion Selectivity                                  Recycling                                                                               Catalyst (g)  (mol %)    (mol %)                                      ______________________________________                                         1        0.39          98.5       96.7                                         2        0.19          95.6       92.8                                         3        0.39          95.8       92.7                                         4        0.39          93.9       89.9                                         5        0.59          95.1       90.5                                         ______________________________________                                     

What is claimed is:
 1. A method for preparing an aromatic secondary amino compound represented by the formula (2) ##STR53## (wherein each R is a hydrogen atom, alkyl group, alkoxy group, amino group, hydroxyl group or fluorine; n is an integer of from 0 to 5; and R' is an alkyl group, phenyl group, benzyl group, naphthyl group, furyl group, furfuryl group or cyclohexyl group, and R' may be substituted by an alkyl group, alkoxy group, phenyl group, phenoxy group, cyclohexyl group, substituted amino group, carboxyl group, hydroxyl group or fluorine) which comprises the step of subjecting, to a dehydrogenation reaction at a temperature of 120° to 250° C., an N-cyclohexylideneamino compound represented by the formula (1) ##STR54## (wherein R, R' and n are defined above) in the presence of a catalytic amount of a platinum group catalyst and a hydrogen acceptor selected from the group of olefin compounds, nitro compounds and phenols wherein the dehydrogenation reaction is conducted in the presence of a sulfur-free polar solvent.
 2. The method for preparing an aromatic secondary amino compound according to claim 1 wherein said dehydrogenation reaction is conducted by simultaneously introducing the N-cyclohexylideneamino compound and the hydrogen acceptor into the sulfur-free polar solvent in which the catalyst is dispersed.
 3. The method for preparing an aromatic secondary amino compound according to claim 1 wherein said dehydrogenation reaction is carried out by adding an alkali metal compound and/or an alkaline earth metal compound as a cocatalyst.
 4. The method for preparing an aromatic secondary amino compound according to claim 3 wherein said dehydrogenation reaction is carried out by simultaneously introducing the N-cyclohexylideneamino compound and the hydrogen acceptor into a mixture obtained by adding the cocatalyst and the platinum group catalyst to the sulfur-free polar solvent. 